It is well known that the transmission and reception of electromagnetic radiation at frequencies such as radio frequencies is severely impaired by any significant mass of solid material such as the walls of a building or the ground above a tunnel. The inability to transmit and/or recieve radio signals within a tunnel or from one part of a building to another can be a severe disadvantage.
In order to mitigate the described disadvantage, it has previously been proposed to establish a distributed antenna system, which system is sometimes referred to as a "leaky feeder". This comprises the provision of a co-axial cable with holes in the shielding of the cable at strategic locations whereby a radio frequency signal injected into the cable "leaks out" at the strategically placed holes. This arrangement does, to some extent, mitigate the above dscribed disadvantage. However, attenuation of the radio frequency signal within the cable is severe and typically a repeater may be required at 100 yard intervals with a maximum practical length of cable being about 1 mile. Beyond this distance, it is extremely difficult to distinguish the original signal from the background noise, despite the use of the repeaters. It will be appreciated that a relatively high power signal is used and consequently the co-axial cable must have relatively high power specifications, which inevitably result in a relatively high expense. The "leaky feeder" co-axial system is not appropriate for use with the radio signals at the frequencies used for cellular radio telephone systems.